When viewing videos, the progressbar / slider is not in sync with the video.

Effect: Irritating/Unexpected behaviour

To reproduce:
1. Start XnView
2. In XnView browser select a short video (e.g. .mov file of 10 seconds. The shorter the video, the better the problem can be seen)
Actual behaviour (bug): The video is shown in the preview. The progressbar/slider doesn't move for an instance although the video is playing, already.
Expected behaviour: Video and progressbar/slider should be in sync.
3. Wait till video is finished.
Actual behaviour (bug): When video is finished, progressbar/slider still hasn't reached 100% - it gets stuck at about 95%.
Expected behaviour: Once the video is finished, progressbar/slider should be at 100%.

I tried with =false and .mp4, Videos won't play at all now. I can progress the video by dragging scrubbar. But no videos play at all. Fullscreen or preview.
I don't know whats going on here. I even put ffmpeg inside addons folder.